title: Staged assembly of histone gene expression machinery at subnuclear foci in the abbreviated cell cycle of human embryonic stem cells.
abstract: Human embryonic stem (hES) cells have an abbreviated G(1) phase of the cell cycle. How cells expedite G(1) events that are required for the initiation of S phase has not been resolved. One key regulatory pathway that controls G(1)/S-phase transition is the cyclin E/CDK2-dependent activation of the coactivator protein nuclear protein, ataxia-telangiectasia locus/histone nuclear factor-P (p220(NPAT)/HiNF-P) complex that induces histone gene transcription. In this study, we use the subnuclear organization of factors controlling histone gene expression to define mechanistic differences in the G(1) phase of hES and somatic cells using in situ immunofluorescence microscopy and fluorescence in situ hybridization (FISH). We show that histone gene expression is supported by the staged assembly and modification of a unique subnuclear structure that coordinates initiation and processing of transcripts originating from histone gene loci. Our results demonstrate that regulatory complexes that mediate transcriptional initiation (e.g., p220(NPAT)) and 3'-end processing (e.g., Lsm10, Lsm11, and SLBP) of histone gene transcripts colocalize at histone gene loci in dedicated subnuclear foci (histone locus bodies) that are distinct from Cajal bodies. Although appearance of CDK2-phosphorylated p220(NPAT) in these domains occurs at the time of S-phase entry, histone locus bodies are formed approximately 1 to 2 h before S phase in embryonic cells but 6 h before S phase in somatic cells. These temporal differences in the formation of histone locus bodies suggest that the G(1) phase of the cell cycle in hES cells is abbreviated in part by contraction of late G(1).
authors.affiliation: Center for Stem Cell Biology and Regenerative Medicine, Department of Cell Biology and Cancer Center, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA.
authors.forename: Prachi N
authors.initials: PN
authors.lastname: Ghule
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Dominski
authors.forename: Xiao-Cui
authors.initials: XC
authors.lastname: Yang
authors.forename: William F
authors.initials: WF
authors.lastname: Marzluff
authors.forename: Klaus A
authors.initials: KA
authors.lastname: Becker
authors.forename: J Wade
authors.initials: JW
authors.lastname: Harper
authors.forename: Jane B
authors.initials: JB
authors.lastname: Lian
authors.forename: Janet L
authors.initials: JL
authors.lastname: Stein
authors.forename: Andre J
authors.initials: AJ
authors.lastname: van Wijnen
authors.forename: Gary S
authors.initials: GS
authors.lastname: Stein
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000235:genetics*; D018797:Cell Cycle Proteins / Q000378:metabolism; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism*; D006657:Histones / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D042581:Intranuclear Space / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D009687:Nuclear Proteins / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism; D039221:mRNA Cleavage and Polyadenylation Factors / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D006657:Histones; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D017411:Ribonucleoproteins, Small Nuclear; D039221:mRNA Cleavage and Polyadenylation Factors; C438196:LSM10 protein, human; C506080:LSM11 protein, human; C101693:NPAT protein, human; C092663:SLBP protein, human